The particular problems encountered in the prior art and in the industry are very well articulated in prior U.S. Pat. No. 4,976,307 which is specifically incorporated herein by reference in its entirety.
The present invention is a further improvement over the embodiments disclosed in that prior patent. As noted therein, the preferred method to return a leaking feed water heater to service is to seal both the inlet and outlet ends of the leaky U-shaped tube at the tube sheet. This is much faster and substantially more economical than replacing the entire tube or the tube bundle. Experience has shown that a feed water heater may be operated economically even when up to 10% of the tubes within the feed water heater have been plugged. If more than 10% of the tubes are plugged, the efficiency of the system declines to a level at which it is more economical to replace or repair the U-shaped tube bundles. An advantage of plugging the ends of the tubes, even when more than 10% have been plugged, is that the removal of the feed water heater from service and subsequent repair or replacement may be planned in advance and executed in an economical, orderly, non-crisis manner.
One difficulty with the plugs disclosed in the prior patent resides in use of internally or externally supplied heat. A heat source must be either provided inside or outside of the plug, which complicates the manufacturing and installation process. Additionally, once these prior art plugs are installed, it is difficult to tell when actual sealing takes place. The plug is merely inserted into a tube, and then sealed. There is no visual indication of a successful seal. Additionally, once these plugs are installed, it is very difficult to remove the plugs when further repair is done to the tube or to the tube sheets.